You need this to limit pressure.
If you are buying any mains pressure Cleanstream kids, then you need a water diverter. Can run the shower at normal pressure, but limit the water coming out the free hose. Superb!
Some kits come with a diverter included it appears now
Easy to install and is to use.
When it first arrived was quite happy but realised it doesn't fit on all showers so had to go and spend more money to find an adapter so that could be used